Suspension devices include multi-link suspensions, in which a damper and a plurality of arms are laid out so that a reaction force acting on the damper (hereafter referred to as a “damper reaction force”) or a lateral force acting on the wheel (i.e., a force in the width direction of the vehicle) acts in the toe-in direction of the wheel.
Specifically, the layout of the arms is configured so that the damper reaction force acts on the rear, with respect to the vehicle, relative to the elastic kingpin axis in order to cause the damper reaction force to act in the toe-in direction of the wheel.
Furthermore, the layout of the arms is configured so that the caster trail is a negative value, i.e., so that the intersection of the elastic kingpin axis and a ground contact surface is positioned to the rear of the vehicle body relative to the ground contact center (contact patch center) of the wheel, in order to cause the lateral force acting on the wheel (i.e., the force in the width direction of the vehicle) to act in the toe-in direction of the wheel.
In this suspension device, in order to cause the damper reaction force or the lateral force acting on the wheel (i.e., the force in the width direction of the vehicle) to act in the toe-in direction, in addition to the layout described above, the elastic kingpin axis is inclined towards the rear side of the vehicle, and the damper is offset rearward of the vehicle relative to the wheel center (e.g., see Patent Reference 1).
With regards to the damper disclosed in Patent Reference 1, an upper end part is connected to a vehicle body, and a lower end part is connected to a knuckle. With regards to the arms, an inner end part is connected to the vehicle body, and an outer end part is connected to the knuckle. When a damper of such description is offset rearwards of the vehicle body relative to the wheel center, the damper reaction force acts as a force that attempts to cause the knuckle to rotate (about the wheel center).
As a result, a torsional force is generated in the arms to prevent rotation of the knuckle. In order for the arms to bear the generated torsional force, it is necessary to set a large outside diameter dimension for each of the arms and increase the stiffness of each of the arms. Also, in an instance in which each of the arms is a tube, it is necessary to set a large wall thickness dimension for each of the arms and increase the stiffness of each of the arms.
However, if a large outside diameter dimension or wall thickness dimension is set for the arms, it is difficult to minimize cost. Also, if a large outside diameter dimension or wall thickness dimension is set for the arms, there is a risk of the unsprung weight increasing, affecting the road-following performance and reducing riding comfort.
Also, in order to prevent rotation of the knuckle, a torsional force is generated in a support bracket that connects each of the arms to the vehicle body side. Therefore, in order for the support brackets to bear the torsional force, it is necessary to increase the stiffness of the support bracket, causing an increase in cost or the vehicle weight.